The invention relates to a mixture comprising an amino resin and a polymer which consists to the extent of at least 80% by weight of C2- to C3-alkylene oxide groups.
The invention also relates to amino resins comprising covalently bonded polymers as defined above. The invention relates in particular to aqueous dispersions of these mixtures with amino resins and to the use of the mixtures, amino resins, and/or their aqueous dispersions as curing agents in coating compositions.
Because of their reactivity, especially to hydroxyl, amino resins are used as curing agents for polymeric binders. In paint chemistry, hydrophobic, water-insoluble amino resins have been found particularly advantageous. In the case of aqueous coating compositions, the use of water-insoluble amino resins is of course more difficult. EP 733 686 discloses dispersing the amino resins with an anionic emulsifier.
The curing agent is added to the coating composition only by the paint manufacturer. In this case it is particularly important to the paint manufacturer that this curing agent can be used both in aqueous coating compositions and in coating compositions which are dissolved in organic solvents. In this context, irrespective of the chosen coating composition, a long shelf life, ready processability and good performance properties of the coatings subsequently obtained should be ensured. In the case of the aqueous amino resin dispersions of EP 733 686, their use in coating compositions based on organic solvents leads to disadvantageous properties, for example deficient water resistance of the resulting coatings.
U.S. Pat. No. 3,310,416 discloses water-insoluble amino resins comprising polyethylene glycols. These amino resins are used as dispersants, for example for hydrocarbons or polysiloxanes.
It is an object of the present invention to provide amino resins which are suitable as curing agents for aqueous coating compositions and for coating compositions based on organic solvents.
We have found that this object is achieved by the initially defined mixtures, amino resins and their aqueous dispersions.
The amino resin which is a constituent of the mixture comprises reaction products of aldehydes, for example glyoxal, furfurol and, preferably, formaldehyde, with amino compounds, such as urea or aminotriazine, for example benzoguanamine, acetoguanamine and, preferably, melamine.
Preference is given to amino resins based on aminotriazines. Reaction products of melamine and formaldehyde are particularly preferred.
In the course of the reaction of aldehyde, especially formaldehyde, the amino groups of the aminotriazines have been alkylolated, especially methylolated; in other words, the hydrogens of the amino groups are replaced by alkylol groups. Preferably more than 30%, in particular more than 50% of the hydrogens are replaced by alkylol groups. As a result, for example, of condensation reactions of the alkylol groups, the amino resins may contain a plurality of aminotriazine rings. Preferably they contain on average from 1 to 20 aminotriazine rings.
The remaining alkylol groups are preferably etherified, extensively or fully, with alcohols, preferably with C1- to C16-alkanols. These are preferably butanol or mixtures of butanol and methanol predominantly containing butanol.
The amino resins are preferably insoluble in water.
The dilution number of the amino resins is preferably less than 20 and, with particular preference, less than 5, in particular less than 2 or 1 g. The dilution number is a measure of how much hydrophilic solvent can be mixed with an amino resin without the resulting solution becoming cloudy.
The dilution number is determined by the following method:
1 g of amino resin is placed in a 25 ml test tube. Then 0.5 g portions of water are added at 23xc2x0 C. After each portion has been added the tube is shaken and observed to see whether clouding or phase separation (incompatibility) remains after shaking. The amount of water, in g, added when incompatibility occurs is the dilution number.
For this purpose the polymer can be added, for example, to the amino resin solution as obtained in the preparation of the amino resin, in an organic solvent, generally the etherifying alcohol.
The resulting mixture can then be converted into an aqueous dispersion of the amino resin by adding water.
The polymer can also, for example, first be dissolved in water and the aqueous solution added to the amino resin.
The resulting aqueous dispersion of the amino resin can then be used as a curing agent in aqueous coating compositions.
In principle it is of course also possible to add the amino resin and the polymer, separately or together, directly to the aqueous coating composition and then to disperse the amino resin therein with the aid of the polymer.
Another embodiment of the invention comprises reacting the polymer with the water-insoluble amino resin; in other words, some of the alkylol groups of the amino resin are etherified with this polymer. This case is also subject to the above statements regarding the amino resin, the polymer and the proportions by weight of the two; in formulae I and II, one of the radicals R1 and R2 is replaced by the bond to the amino resin. The amino resin obtained by reaction with the polymer is still insoluble in water and has the above dilution number, but can be dispersed in water, as described above for the mixture, and is used accordingly as a curing agent in coating compositions.
Coating compositions comprise a polymeric binder with or without further additives such as pigments, dyes, leveling agents, thickeners, etc.
The polymeric binder, owing to its content of active hydrogens (OH, NH, SH groups), can be crosslinked with amino resins, i.e. is curable.
Examples of suitable binders are alkyd, polyester, epoxy and polyurethane resins, free-radical polymers based on acrylates, vinyl esters, dienes and vinylaromatic compounds or mixtures thereof.
In addition to the amino resin, the novel mixture comprises a polymer which consists to the extent of at least 80% by weight, preferably to the extent of at least 90% by weight, of C2- to C3-alkylene oxide groups. These groups can be exclusively ethylene oxide groups, propylene oxide groups, or ethylene oxide and propylene oxide groups.
The polymer preferably contains on average at least 10 and, with particular preference, at least 20 alkylene oxide groups. The maximum number of these groups is preferably 500, particularly preferably 300 and, with very particular preference, 200.
Preferred polymers are those of the formulae 
where R1 and R2 independently are hydrogen, C1- to C20-alkyl or C1- to C20-acyl.
Preferably, R1 and R2 are hydrogen or C1-C4-alkyl, especially methyl or n-butyl.
The variables x, y, z are preferably at least 1. Preferably therefore, both formula I and formula II represent 3-block copolymers (EO-PO-EO in formula I and PO-EO-PO in formula II).
Polymers of this kind are known and are obtainable commercially from BASF, for example, under the designation Pluronic(copyright).
The content of the polymer in the mixture is preferably from 0.1 to 50 parts by weight, particularly preferably from 0.5 to 10 parts by weight, based on 100 parts by weight of amino resin.
The polymer serves as an emulsifier, in other words a dispersant, for dispersing the water-insoluble amino resin in water.
Preference is given to free-radical addition polymers, condensation polymers or polyaddition polymers having OH groups, preferably with a hydroxyl number of from 20 to 200 mg of KOH/g of solid matter (in accordance with DIN 53240).
The binder and therefore the coating compositions as well can be present, for example, in the form of solutions in water or organic solvents or in the form of aqueous dispersions.
A significant advantage of the invention is that the novel mixtures and the novel amino resins modified with the polymers, or the aqueous dispersions of these mixtures and amino resins, can be used as curing agents both for aqueous coating compositions and for coating compositions in organic solvents, and in both cases give coatings having good performance properties, in particular good water resistance and adhesion.
The aqueous dispersions of the mixtures or of the polymer-modified amino resins are stable on storage. The coating compositions which comprise the mixtures or the polymer-modified amino resins are also stable on storage.
The novel coating compositions which comprise a polymeric binder and the novel curing agent can be applied to any desired substrates, for example of wood, metal, paper or plastic, by any desired methods, for example spreading, knife coating or spraying.
Following application, curing and removal of water and/or organic solvent take place in general by drying at elevated temperatures or by stoving.